A visual, position-independent instrumental reinforcer devaluation task for rats

Abstract

Flexible goal-directed behavior has been studied across species using reinforcer devaluation tasks, in which subjects form associations between specific stimuli (cues) and specific reinforcer(s). The reinforcer is subsequently devalued by selective satiation or taste aversion. Following devaluation, subjects adjust their responding to the cues reflecting the new value of the reinforcer. Tasks currently used in rats differ in several ways from tasks used in monkeys and this may explain contrasting results between the two species. To address one of the differences, we developed a rat task independent of spatial cues. It employs two visual cues presented simultaneously, changing left and right positions pseudorandomly. Each cue predicts one of two food reinforcers. Rats were trained to lever press in response to the two visual cues. Subsequently, they were satiated on one of the foods followed by an extinction test where in each trial they could choose to respond to one of the two cues, one predicting the devalued reinforcer and the other the non-devalued. This procedure was repeated later with the alternative food devalued. The rats adjusted their responding by choosing the cue predicting the devalued food significantly less (p<0.05) than the alternative cue. These results show that rats can discriminate two visual stimuli presented simultaneously, devalue two different foods by selective satiation, and transfer the new value to the visual cues. Discrimination of the visual cues is not aided by spatial cues, thereby eliminating a major difference between the instrumental tasks used in rats and the task used in monkeys.